I lube it all with Mobil 1 engine oil. The oil is formulated to deal with carbon in an internal combustion engine-which is essentially what you have with an AR. When I clean, I use WD40 for solvent. What doesn't come off with a good wiping I leave.
If you look at a heavily carboned bolt tail you will see where the carrier rides-there is very little carbon where the carrier touches because the carrier keeps it rubbed off WHERE IT MATTERS. The carbon around the skirt leading up to the rings doesn't matter. In my experience it will only build up so much, but I do clean mine after every outing, whether it saw 500 rds or just 50. Again, I clean by spraying with WD40 and wiping away the soot and carbon, then blow off with compressed air. Lube liberally with Mobil 1 and re-assemble.
ETA: I do not remove rings unless there's a problem